Lens frame guiding mechanism of a zoom lens

ABSTRACT

A lens frame guiding mechanism of a zoom lens includes lens frames having projections which extend radially outwards, wherein a cam follower is formed on each projection; a linear guide barrel; linear guide slots formed on the linear guide barrel parallel to the optical axis, wherein the projections of each lens frame are respectively engaged in the linear guide slots to be slidable therealong; a cam barrel fitted outside the linear guide barrel to be relatively rotatable about the optical axis thereto; and bottomed cam grooves formed on an inner peripheral surface of the cam barrel, in which the cam followers of a corresponding lens frame are respectively engaged. The lens frames are moved in the direction of the optical axis, without rotating about the optical axis, to change a focal length of said zoom lens via rotation of said cam barrel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens (a zoom lens barrel), andmore specifically to a mechanism for guiding more than one lens frame inthe direction of the optical axis of the zoom lens.

2. Description of the Related Art

It is known in the art for a zoom lens, or a zoom lens barrel, having amechanism which guides a plurality of lens frames (lens groups) in theoptical axis direction of the zoom lens without rotating about theoptical axis, so that the plurality of lens frames are driven in theoptical axis direction in a predetermined moving manner by rotation of acam barrel having cam grooves. In such a conventional lens guidingmechanism, the plurality of lens frames are individually guided alongthe optical axis without rotating about the optical axis, while theplurality of lens frames are driven in the optical axis direction in apredetermined moving manner in accordance with the contours of the camgrooves of the cam barrel. Such a conventional lens frame guidingmechanism has no substantial adverse effects if it is used for the zoomlens of a conventional camera using light-sensitive film such as 35 mmor APS compact zoom camera.

However, such a conventional lens frame guiding mechanism does havesubstantial adverse effects if it is used for the zoom lens of a digitalcamera because object images are formed on the sensitive surface of asmall CCD (CCD image sensor) which is much smaller than the pictureplane of conventional cameras using light sensitive film. Namely, uponassembly, every lens element of a digital camera must be opticallycentered, correctly spaced, and held firmly with a relatively highprecision, e.g., tens times greater than that required in conventionalcameras using light-sensitive film. For instance, if the angle of viewis constant, the focal length of a photographing lens becomes shorter asthe size of the picture plane reduces, which in turn reduces the sizesof all the elements of the photographing lens such as, e.g., lenselements, lens frames. Therefore, the influence that a tolerance (e.g.,10 μm) has on a photographing lens system of a digital camera is muchlarger than the influence that the same tolerance would have on aphotographing lens system of a conventional camera using light-sensitivefilm. Accordingly, manufacturing or assembling error which falls withintolerance of optical performance in the photographing optical system ofa conventional camera using light-sensitive film can be outside thetolerance of optical performance in the photographing optical system ofa digital camera. Specifically in a photographing lens system of adigital camera, the influence that eccentricity or tilt of one or morelens frames (one or more lens groups) relative to another lens frame orframes (lens group or groups) has upon the optical performance of thephotographing optical system is larger than the influence of deviationof one or more lens frames (one or more lens groups) in the optical axisdirection relative to another lens frame or frames (another lens groupor groups).

From this point of view, in the conventional lens frame guidingmechanism, a manufacturing or assembling error of each element of thezoom lens tends to exert adverse effects upon the optical performance ofthe photographing optical system since a plurality of lens frames areindependently guided in the optical axis direction without rotatingabout the optical axis. For instance, if there is positional error suchas eccentricity in each of the lens frames, the linear guide member, andthe cam barrel, there is a possibility of these errors being accumulatedto deteriorate the optical performance of the photographing opticalsystem, especially in the case of eccentricity of one or more lensgroups relative to another lens group or groups.

SUMMARY OF THE INVENTION

The present invention has been device in view of the above-mentionedproblems; accordingly, an object of the present invention is to providea lens frame guiding mechanism, used in a zoom lens, which guides aplurality of lens frames in the optical axis direction of the zoom lenswithout rotating about the optical axis so that the plurality of lensframes are driven in the optical axis direction by rotation of a cambarrel having cam grooves, wherein eccentricity of one or more lensgroups relative to another lens group or groups does not occur easily.

To achieve the object mentioned above, according to an aspect of thepresent invention, a lens frame guiding mechanism of a zoom lens isprovided, including a plurality of lens frames each having a pluralityof projections which extend radially outwards at predetermined intervalsin a circumferential direction, wherein a cam follower is formed on eachof the projections; a linear guide barrel provided around the pluralityof lens frames, wherein the linear guide barrel is guided along theoptical axis of the zoom lens without rotating; a plurality of linearguide slots formed on the linear guide barrel to extend parallel to theoptical axis, wherein the number of the plurality of linear guide slotscorresponds to the number of the plurality of projections of each of thelens frames so that the plurality of projections of each of the lensframes are respectively engaged in the plurality of linear guide slotsto be slidable in a direction of the optical axis; a cam barrel fittedoutside the linear guide barrel to be rotatable about the optical axisrelative to the linear guide barrel; and a plurality of bottomed camgrooves formed on an inner peripheral surface of the cam barrel for eachof the plurality of lens frames, in which the plurality of cam followersof a corresponding lens frame of the plurality of lens frames arerespectively engaged, wherein the profiles of the cam grooves for one ofthe plurality of lens frames is different from the profiles of the camgrooves for the other of the plurality of lens frames. The plurality oflens frames are moved in the direction of the optical axis, withoutrotating about the optical axis, to change a focal length of the zoomlens via rotation of the cam barrel.

Preferably, the number of projections of each of the lens frames, thenumber of the linear guide slots of the linear guide barrel, and thenumber of the bottomed cam grooves of the cam barrel are three,respectively arranged at 120° equi-angular intervals.

Preferably, the cam barrel is fitted on the linear guide barrel so as tobe immovable in the direction of the optical axis relative to the linearguide barrel.

Preferably, each of the plurality of projections is formed to haveopposite faces extending parallel to each other so that the oppositefaces are respectively in sliding contact with side faces of acorresponding linear guide slot of the plurality of linear guide slots.

In an embodiment, the zoom lens is incorporated in a digital camera.

According to another aspect of the present invention, a lens frameguiding mechanism of a zoom lens is provided, including a first lensframe having a first group of three projections extending radiallyoutwards at equi-angular intervals, each of the first group of threeprojections having a first cam follower; a second lens frame having asecond group of three projections extending radially outwards atequi-angular intervals, each of the second group three projectionshaving a second cam follower; a linear guide barrel provided around thefirst lens frame and the second lens frame, and guided in a direction ofthe optical axis without rotating about the optical axis; three linearguide slots formed on the linear guide barrel so as to extend parallelto the optical axis, the first group of three projections and the secondgroup of three projections being slidably engaged in the three linearguide slots, respectively; a cam barrel fitted on the linear guidebarrel to be rotatable about the optical axis relative to the linearguide barrel; a first group of three cam grooves which are formed on aninner peripheral surface of the cam barrel so that the three first camfollowers are respectively engaged in the first three cam grooves; and asecond group of three cam grooves which are formed on the innerperipheral surface of the cam barrel so that the three second camfollowers are respectively engaged in the second group of three camgrooves. The first and second lens frames are moved in the direction ofthe optical axis, without rotating about the optical axis, in apredetermined moving manner to change a focal length of the zoom lens byrotation of the cam barrel.

The present disclosure relates to subject matter contained in JapanesePatent Application No.2000-24039 (filed on Feb. 1, 2000) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is an exploded perspective view of an embodiment of a zoom lensaccording to the present invention, showing the overall structurethereof;

FIG. 2 is an axial cross sectional view of the zoom lens shown in FIG.1, showing the zoom lens above the optical axis thereof;

FIG. 3 is a developed view of the inner peripheral surface of a firstcam barrel, showing the contours of first and second cam grooves formedon the inner peripheral surface of the first cam barrel;

FIG. 4 is an exploded perspective view of the first cam barrel shown inFIG. 3, a linear guide barrel, a first lens frame and a second lensframe;

FIG. 5 is a fragmentary rear view of the linear guide barrel and thefirst lens frame, showing the periphery of an insertion groove of thelinear guide barrel;

FIG. 6 is an exploded perspective view of the linear guide barrel, alinear guide ring and a retainer ring;

FIG. 7 is a developed view of the linear guide barrel, the linear guidering and the retainer ring;

FIG. 8 is a developed view of a second cam barrel and a barrier drivering, showing the positional relationship therebetween when the zoomlens is set at the telephoto extremity thereof (when the zoom lens is ina ready-to-photograph state);

FIG. 9 is a developed view of the second cam barrel and the barrierdrive ring, showing the positional relationship therebetween when thezoom lens is positioned in the accommodation position (when the power ofthe zoom lens is turned OFF);

FIG. 10 is an axial cross sectional view of the zoom lens shown in FIG.1, showing the zoom lens above the optical axis thereof, showing thepositional relationship between an external barrel and the second cambarrel (a first lens group) when the zoom lens is set at the wide-angleextremity thereof;

FIG. 11 is an axial cross sectional view of the zoom lens shown in FIG.1, showing the zoom lens above the optical axis thereof, and showing thepositional relationship between the external barrel and the second cambarrel (the first lens group) when the zoom lens is set at the telephotoextremity thereof;

FIG. 12 is an explanatory view showing variations in axial position ofthe sensitive surface (image plane) of a CCD, the first lens group, asecond lens group, and a barrier block when the zoom lens is driven fromthe accommodation position to the telephoto extremity and thereafter tothe wide-angle extremity;

FIG. 13 is an exploded perspective view of the barrier block, viewedfrom behind the barrier block;

FIG. 14 is a perspective view of the barrier block with an annularpressure plate being removed from the barrier block, viewed from behindthe barrier block;

FIG. 15A is a schematic front view of the barrier block, showing twopairs of barrier blades in a fully open position;

FIG. 15B is a schematic front view of the barrier block, showing the twopairs of barrier blades in a half-closed position;

FIG. 15C is a schematic front view of the barrier block, showing the twopairs of barrier blades in a fully closed position;

FIG. 16 is a perspective view of the second cam barrel and the barrierdrive ring, showing the positional relationship between a driven leverwhich extends from the barrier drive ring and a rotation transfer recessformed on the second cam barrel;

FIG. 17 is a front view of the external barrel that is supported by theexternal barrel to be freely rotatable about the optical axis, in astate where the barrier drive ring is rotated to one rotational limitthereof to thereby fully close the two pairs of barrier blades; and

FIG. 18 is a front view of the external barrel shown in FIG. 17, in astate where the barrier drive ring is rotated to the other rotationallimit thereof to thereby fully open the two pairs of barrier blades.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of a zoom lens (zoom lens barrel) according tothe present invention that is incorporated in a digital camera will behereinafter discussed. Firstly, the overall structure of the zoom lenswill be discussed with reference mainly to FIGS. 1 and 2. In thedrawings and the following descriptions, symbols “(F)”, “(L)” and “(RL)”which are each appended as a suffix to the reference numeral of someelements of the zoom lens barrel indicate that the element isstationary, the element is movable linearly along an optical axis O ofthe zoom lens without rotating about the optical axis O, and the elementis movable along the optical axis O while rotating about the opticalaxis O, respectively.

The photographic optical system of the zoom lens includes three lensgroups; namely, a first lens group (front lens group) L1 (L), a secondlens group (middle lens group) L2 (L) and a third lens group (rear lensgroup) L3 (L), in this order from the object side (the left side asviewed in FIG. 2). The zoom lens performs zooming by moving the firstand second lens groups L1 and L2 along the optical axis O relative tothe sensitive surface of a stationary CCD 12 a (see FIG. 1) and at thesame time changing the space between the first and second lens groups L1and L2 in a predetermined manner. The zoom lens performs a focusingoperation by moving the third lens group L3 along the optical axis O tobring an object into focus. The third lens group L3 functions as afocusing lens group which is driven along the optical axis Oindependently of the axial position of each of the first and second lensgroups L1 and L2. Thus, the zoom lens is an internal-focusing type zoomlens having a lens construction which allows the focus to be altered bymoving the rearmost lens group provided as a focusing lens groupinternally within the lens barrel.

The zoom lens is provided with a housing 10(F) which is fixed to acamera body of a digital camera (not shown). The housing 10 can beintegral with the camera body to be provided as an element thereof. Thezoom lens is provided in the housing 10 with a stationary barrel 11(F)that is fixed to the housing 10. The stationary barrel 11 is provided onan outer peripheral surface thereof with a fine male thread 11 a. Thestationary barrel 11 is provided on an inner peripheral surface thereofwith a female helicoid (female helicoidal thread) 11 b and three linearguide grooves 11 c (only one is shown in FIG. 1) extending parallel tothe optical axis O , i.e., extending in the optical axis direction. Thethree linear guide grooves 11 c are formed to cut across the femalehelicoid 11 b. The three linear guide grooves lic are formed at 120°intervals (i.e., at an equi-angular distance) about the axis of thestationary barrel 11.

As shown in FIG. 2, the housing 10 is provided with a CCD insertionopening 10 a, a filter fixing portion lOb and a focusing lens groupguide portion 10 c. The CCD 12 a which is fixed to a substrate 12 ispositioned in the CCD insertion opening 10 a. A filter 10 d such as alow-pass filter is fixed to the filter fixing portion 10 b. The thirdlens group L3 is guided by the focusing lens group guide portion 10 c tobe movable in the optical axis direction. The axial position of thethird lens group L3 on the optical axis O is determined by the directionof rotation of a feed screw 10 e and the angle of rotation (amount ofrotation) thereof. The feed screw 10 e extends parallel to the opticalaxis O from the camera body in the focusing lens group guide portion 10c. The feed screw Oe is driven by a pulse motor (not shown) provided inthe camera body. The angle of rotation of the feed screw 10 e iscontrolled via an encoder (not shown) of the pulse motor.

The zoom lens is provided on the stationary barrel 11 with a rotationalbarrel 13 (RL). The rotational barrel 13 is provided on an innerperipheral surface thereof with a fine female thread 13 a which mesheswith the fine male thread 11 a of the stationary barrel 11. Therotational barrel 13 is provided on an outer peripheral surface thereofwith a circumferential gear 13 b (see FIG. 1). The rotational barrel 13is driven to rotate about the optical axis O by a drive pinion (notshown) which meshes with the circumferential gear 13 b. When therotational barrel 13 is driven to rotate about the optical axis O, therotational barrel 13 moves in the optical axis 10 direction whilerotating about the optical axis O in accordance with the engagement ofthe fine female thread 13 a with the fine male thread 11 a. Therotational barrel 13 is provided at the front end of an inner peripheralsurface thereof with three inward projections 13 c at 120° intervalsabout the axis of the rotational barrel 13. As shown in FIG. 1, aflexible coding plate 14 (RL) is fixed on an outer peripheral surface ofthe rotational barrel 13 along a circumference thereof, while a brush 15(F) that is in contact with the coding plate 14 is fixed to the housing10. The brush 15 remains in sliding contact with the coding plate 14regardless of a movement of the coding plate 14 relative to the brush 15when the coding plate 14 moves in the optical axis direction inaccordance with the engagement of the fine female thread 13 a with thefine male thread 11 a, so as to sense the rotational position of therotational barrel 13 as digital and/or analogue information. The finefemale thread 13 a, which is provided on the rotational barrel 13, isprovided as a device for supporting the rotational barrel 13 on thestationary barrel 11 so that the rotational barrel 13 can rotate freelyabout the optical axis O on the stationary barrel 11. However,alternatively, the rotational barrel 13 can be supported on thestationary barrel 11 so as to be able to rotate freely about the opticalaxis O without moving in the optical axis direction relative to thestationary barrel 11.

The zoom lens is further provided with a linear guide barrel 16 (L), afirst cam barrel 17 (RL) and a second cam barrel 18 (RL). The first cambarrel 17 is fitted on the linear guide barrel 16 to be rotatable aboutthe optical axis O relative to the linear guide barrel 16 and to beimmovable in the optical axis direction relative to the linear guidebarrel 16. The second cam barrel 18 is fitted on the front end of thefirst cam barrel 17 to be rotatable together with the first cam barrel17 about the optical axis O and also to be movable in the optical axisdirection relative to the first cam barrel 17. The linear guide barrel16, the first cam barrel 17 and the second cam barrel 18 are assembledin advance as a unit, and the rear of this barrel unit is positioned inthe stationary barrel 11.

The linear guide barrel 16 is provided at the rear end thereof with anouter flange 16 a. A linear guide ring (flange ring) 19(L) is fixed tothe front end of the linear guide barrel 16 via a retainer ring 20(L).The first cam barrel 17 is held between the outer flange 16 a and thelinear guide ring 19, and is rotatable about the optical axis O relativeto the linear guide barrel 16 and also movable together with the linearguide barrel 16 in the optical axis direction.

The second cam ring 18, which is fitted on the front end of the firstcam barrel 17, is provided at the rear end thereof with three linearguide portions 18 a (only two are shown in FIG. 1) at 120° intervalsabout the axis of the second cam ring 18. Each of the three linear guideportions 18 a is provided with a spring holding groove 18 a 1, and apair of guide grooves 18 a 2 positioned on the opposite sides of thespring holding groove 18 a 1 in a circumferential direction of thesecond cam ring 18 (see FIGS. 8 and 9). Each of the three linear guideportions 18 a is further provided, in each spring holding groove 18 a 1at the front end (the left end as viewed in FIG. 8 or 9) of each springholding groove 18 a 1, with an engaging projection 18 a 3. All of thespring holding grooves 18 a 1 and the pairs of guide grooves 18 a 2extend parallel to the optical axis O. The first cam barrel 17 isprovided on an outer peripheral surface thereof with three stopperportions 17 a (only two are shown in FIG. 1) at 120° intervals about theaxis of the first cam barrel 17. Each of the three stopper portions 17 ais provided with a stopper projection 17 a 1, and a pair of guideprojections 17 a 2 positioned on the opposite sides of the stopperprojection 17 a 1 in a circumferential direction of the first cam barrel17 (see FIG. 4). Each pair of guide projections 17 a 2 of the first cambarrel 17 are respectively fitted in the corresponding pair of guidegrooves 18 a 2 of the second cam ring 18 to be slidable in the opticalaxis direction relative to the second cam ring 18, with a compressionspring 21 being held between each engaging projection 18 a 3 and thecorresponding stopper projection 17 a 1. Due to this structure, thesecond cam barrel 18 can slide on the first cam barrel 17 in the opticalaxis direction without rotating about the optical axis O relative to thefirst cam barrel 17. The compression springs 21 constatntly bias thesecond cam barrel 18 toward the front of the zoom lens, so that thefront end of the second cam barrel 18 is usually in press-contact withthe linear guide ring 19. The second cam barrel 18 can move rearward,toward the rear of the zoom lens, against the spring force of thecompression springs 21 by an amount of movement corresponding to apredetermined clearance in the optical axis direction between the guidegrooves 18 a 2 and the guide projections 17 a 2. The second cam barrel18 can also be slightly inclined with respect to the first cam barrel 17(i.e., with respect to the optical axis O) by an amount of inclinationcorresponding to a predetermined clearance in a radial direction betweenthe inner peripheral surface of the second cam barrel 18 and thecorresponding outer peripheral surface of the first cam barrel 17.

The first cam barrel 17 is provided on an outer peripheral surfacethereof with a male helicoid (male helicoidal thread) 17 b that isengaged with the female helicoid 11 b of the stationary barrel 11, andthree rotation transmission grooves 17 c that extend parallel to theoptical axis O. The three rotation transmission grooves 17 c are formedso as to cut across the male helicoid 17 b. The three rotationtransmission grooves 17 c are formed at 120° intervals about the axis ofthe first cam barrel 17. The three inward projections 13 c of therotational barrel 13 are respectively engaged with the three rotationtransmission grooves 17 c to be relatively slidable to each other. Thelinear guide barrel 16 is provided on the outer flange 16 a thereof withthree linear guide projections 16 b at 120° intervals about the axis ofthe linear guide barrel 16. Each linear guide projection 16 b extendsradially outwards to be engaged with the corresponding linear guidegroove 11 c of the stationary barrel 11. The linear guide barrel 16 isfurther provided with three linear guide slots 16 c at 120° intervalsabout the axis of the linear guide barrel 16 so that the circumferentialpositions of the three linear guide slots 16 c coincide with those ofthe three linear guide projections 16 b. Each of the three linear guideslots 16 c penetrates the linear guide barrel 16 radially and extendsparallel to the optical axis O.

As can be seen in FIGS. 4, 5 and 6, each of the three linear guide slots16 c opens at the rear end of the linear guide barrel 16, and the rearend of each linear guide slot 16 c is covered by the corresponding partof the outer flange 16 a and the corresponding linear guide projection16 b at the radially outer side of the linear guide barrel 16. The outerflange 16 a is provided with three insertion grooves 16 h whichrespectively extend along a portion of each three linear guide slots 16c from the front end of the outer flange 16 a to each respective rearend of the three linear guide slots 16 c (i.e., the rear end of theouter flange 16 a), so that a follower pin (cam follower) 22 d and afollower pin (cam follower) 23 d can be inserted into each linear guideslot 16 c from the corresponding insertion groove 16 h.

When the barrel unit which includes the linear guide barrel 16, thefirst cam barrel 17 and the second cam barrel 18 is coupled to thestationary barrel 11 and the rotational barrel 13, each of the threelinear guide projections 16 b of the linear guide barrel 16 is insertedinto the corresponding linear guide groove 11 c of the stationary barrel11 via a corresponding introducing groove 11 d formed on an innerperipheral surface of the stationary barrel 11, and each of the threeinward projections 13 c of the rotational barrel 13 is inserted into thecorresponding rotation transmission groove 17 c of the first cam barrel17 via a corresponding introducing groove 17 d formed on an outerperipheral surface of the first cam barrel 17. After each linear guideprojection 16 b and each inward projection 13 c are inserted into thecorresponding linear guide groove 11 c and the corresponding rotationtransmission groove 17 c,respectively, the female helicoid 11 b of thestationary barrel 11 and the male helicoid 17 b of the first cam barrel17 mesh with each other.

FIG. 2 shows a state where the barrel unit, which includes the linearguide barrel 16, the first cam barrel 17 and the second cam barrel 18,has been coupled to the stationary barrel 11 and the rotational barrel13. In this state, rotating the rotational barrel 13 about the opticalaxis O via the gear 13 b causes the rotational barrel 13 to move in theoptical axis direction while rotating about the optical axis O due tothe engagement of the fine female thread 13 a with the fine male thread11 a. At the same time, the rotation of the rotational barrel 13 istransmitted to the first cam barrel 17 and the second cam barrel 18,which is fitted on the first cam barrel 17, due to the engagement of theinward projections 13 c with the rotation transmission grooves 17 c, sothat the first cam barrel 17 and the second cam barrel 18 rotate aboutthe optical axis O. At this time, the first cam barrel 17 and the secondcam barrel 18 also move in the optical axis direction O due to theengagement of the male helicoid 17 b with the female helicoid 11 b.Furthermore, the linear guide barrel 16 moves in the optical axisdirection without rotating about the optical axis O due to theengagement of the linear guide projections 16 b with the linear guidegrooves 11 c, and at the same time the first and second cam barrels 17and 18, which rotate about the optical axis O relative to the linearguide barrel 16, move together with the linear guide barrel 16 in theoptical axis direction.

The first cam barrel 17 is provided on an inner peripheral surfacethereof with three first cam grooves 17C1 for driving the first lensgroup L1, and three second cam grooves 17C2 for driving the second lensgroup L2. FIG. 3 is a developed view of the inner peripheral surface ofthe first cam barrel 17, showing the contours of the first and secondcam grooves 17C1 and 17C2. The three first cam grooves 17C1 are formedon the inner peripheral surface of the first cam barrel 17 at 120°intervals about the axis of the first cam barrel 17. Likewise, the threesecond cam grooves 17C2 are formed on the inner peripheral surface ofthe first cam barrel 17 at 120° intervals about the axis of the firstcam barrel 17. Each of the first and second cam grooves 17C1 and 17C2has three predetermined positions: an accommodation position, atelephoto position and a wide-angle, in this order along the directionof rotation of the first cam barrel 17 (the vertical direction as viewedin FIG. 3). The telephoto position shown in FIG. 3 of each cam groove17C1 and 17C2 determines the telephoto extremity of the correspondinglens groups L1 and L2, respectively; the wide-angle position of each camgroove 17C1 and 17C2 determines the wide-angle extremity of thecorresponding lens groups Li and L2, respectively; and the accommodationposition of each cam groove 17C1 and 17C2 determines the position of thecorresponding lens groups L1 and L2, respectively, when the power of thedigital camera is turned OFF. The angle of rotation from theaccommodation position to the wide-angle extremity position is shown by“A” in FIG. 3.

The zoom lens is provided with a first lens frame 22(L) and a secondlens frame 23(L) which support the first lens group L1 and the secondlens group L2, respectively. The first lens frame 22 is guided by thefirst cam grooves 17C1 and the linear guide slots 16 c to be movable inthe optical axis direction without rotating about the optical axis O.Likewise, the second lens frame 23 is guided by the second cam grooves17C2 and the linear guide slots 16 c to be movable in the optical axisdirection without rotating about the optical axis O. The first lensframe 22 is provided with three resilient extending pieces 22 b whichextend rearward from a cylindrical portion 22 a of the first lens frame22. The three resilient extending pieces 22 b are formed on the firstlens frame 22 at 120° intervals about the axis of the first lens frame22. Each resilient extending piece 22 b is provided on a radially outersurface thereof with a square projection 22 c which extends radiallyoutwards to be fitted in the corresponding linear guide slot 16 c in aslidable manner in the optical axis direction. Each resilient extendingpiece 22 b is further provided on top of each square projection 22 cwith the follower pin (cam follower) 22 d, which is fixed to theresilient extending piece 22 b to extend radially outwards. Each squareprojection 22 c is formed so that the opposite faces thereof, which arerespectively in sliding contact with the side faces of the correspondinglinear guide slot 16 c, extend parallel to each other. The zoom lens isprovided with a first lens holder 22 e which encloses the first lensgroup L1 to hold the same. The first lens holder 22 e is fixed to thecylindrical portion 22 a of the first lens frame 22 via male and femalethreads 22 f which are formed on an outer peripheral surface of thefirst lens holder 22 e and an inner peripheral surface of thecylindrical portion 22 a, respectively. The position of the first lensgroup L1 relative to the first lens frame 22 in the optical axisdirection can be adjusted by varying the amount of engagement betweenthe male and female threads 22 f. A wave washer 22 h is held between theholder 22 e and an inner flange 22 g of the first lens frame 22 toremove the play between the first lens holder 22 e (or the first lensgroup L1) and the first lens frame 22 (see FIG. 2).

The second lens frame 23 is provided with three resilient extendingpieces 23 b which extend forward from an annular plate portion 23 a ofthe second lens frame 23. The three resilient extending pieces 23 b areformed on the second lens frame 23 at 120° intervals about the axis ofthe second lens frame 23. Each resilient extending piece 23 b isprovided on a radially outer surface thereof with a square projection 23c which extends radially outwards to be fitted in the correspondinglinear guide slot 16 c in a slidable manner in the optical axisdirection. Each resilient extending piece 23 b is further provided ontop of each square projection 23 c with the aforementioned follower pin23 d, which is fixed to the resilient extending piece 23 b to extendradially outwards. The square projections 23 c and the follower pins 23d of the second lens frame 23 are identical to the square projections 22c and the follower pins 22 d of the first lens frame 22 except that theresilient extending pieces 23 b of the second lens frame 23 extend inthe direction opposite to the resilient extending pieces 22 b of thefirst lens frame 22 in the optical axis direction. The zoom lens isprovided with a second lens holder 23 e which encloses the second lensgroup L2 to hold the same. The second lens holder 23 e is fixed to theannular plate portion 23 a of the second lens frame 23 via set screws 23f. A shutter block 24 is provided around the second lens group L2. Theshutter block 24 is fixed to the annular plate portion 23 a of thesecond lens frame 23 via the set screws 23 f that are screwed into therear of the shutter block 24. The shutter block 24 functions tointerrupt light bundles which are incident on the CCD 12 a at a shutterrelease operation.

Each of the first and second lens frames 22 and 23 is guided linearly inthe optical axis direction without rotating about the optical axis O bythe engagement of each of the three square projections 22 c andcorresponding each of the three square projections 23 c with each commoncorresponding linear guide slot of the three linear guide slots 16 c.Each follower pin 22 d penetrates the corresponding linear guide slot 16c of the linear guide barrel 16 to be engaged with the correspondingfirst cam groove 17C1 of the first cam barrel 17, which is fitted on thelinear guide barrel 16 to be rotatable about the optical axis relativeto linear guide barrel 16. Likewise, each follower pin 23 d penetratesthe corresponding linear guide slot 16 c of the linear guide barrel 16to be engaged with the corresponding second cam groove 17C2 of the firstcam barrel 17. When the first and second lens frames 22 and 23 areplaced in the linear guide barrel 16 and the first cam barrel 17,firstly each of the three square projections 22 c and corresponding oneof the three square projections 23 c are inserted into a correspondinglinear guide slot of the three linear guide slots 16 c from the rear endface of the linear guide barrel 16. At the same time, each of the threefollower pins 22 d and corresponding one of the three follower pins 23 dare inserted into corresponding one of the three insertion grooves 16 hto be fitted in the corresponding first and second cam grooves 17C1 and17C2, respectively. It should be noted that the hatched areas of thefirst and second cam grooves 17C1 and 17C2 in FIG. 3 are used solely forthe purpose of inserting each follower pin 22 d or 23 d into thecorresponding cam groove 17C1 or 17C2 during assembly, and thus are notused when the zoom lens is in operation.

According to the above described guide structure, rotating therotational barrel 13 about the optical axis O causes the barrel unitwhich includes the linear guide barrel 16, the first cam barrel 17 andthe second cam barrel 18 to move in the optical axis direction. Duringthis movement of the barrel unit, the first and second cam barrels 17and 18 rotate together about the optical axis O, but the linear guidebarrel 16 does not rotate about the optical axis O. As a result, thefirst lens frame 22 (the first lens group L1) and the second lens frame23 (the second lens group L2) linearly move in the optical axisdirection while changing the space therebetween in accordance with thecontours of the first and second cam grooves 17C1 and 17C2 to therebycarry out a zooming operation.

The coupling structure of the linear guide ring 19 and the retainer ring20 to the front end of the linear guide barrel 16 will be hereinafterdiscussed with reference to FIGS. 6 and 7. The linear guide barrel 16 isprovided, at the front end thereof at 120° intervals about the axis ofthe linear guide barrel 16, with three engaging lugs 16 d each of whichextends radially outwards. A receiving area 16 e is formed between anytwo adjacent engaging lugs 16 d of the linear guide barrel 16 in orderto receive one of three radially inward projections 19 a of the linearguide ring 19. The linear guide barrel 16 is provided immediately behindthe three engaging lugs 16 d with three grooves 16 f, respectively. Theradius of the linear guide barrel 16 from the axis of the linear guidebarrel 16 to the bottom surface of each groove 16 f is identical to theradius from the axis of the linear guide barrel 16 to the surface ofeach receiving area 16 e. The linear guide barrel 16 is provided behindthe three engaging lugs 16 d with three recesses 16 g, respectively,each of which is connected with the corresponding groove 16 f. Eachrecess 16 g is recessed rearward (toward the right as viewed in FIG. 7)in the direction parallel to the optical axis O, i.e., in the opticalaxis direction.

On the other hand, the linear guide ring 19 is provided with theaforementioned three inward projections 19 a at 120° intervals about theaxis of the linear guide ring 19. The three inward projections 19 a canbe inserted into the three receiving areas 16 e, respectively. If thelinear guide ring 19 is rotated about the axis thereof clockwise asviewed in FIG. 6 relative to the linear guide barrel 16 with the threeinward projections 19 a being properly inserted into the three receivingareas 16 e, respectively, each inward projection 19 a slides into thecorresponding groove 16 f. The linear guide ring 19 is provided withthree radially outward projections 19 b at 120° intervals about the axisof the linear guide ring 19. The circumferential positions of the threeoutward projections 19 b are precisely determined with reference to thecircumferential positions of the three inward projections 19 a.

The retainer ring 20 is provided with radially inward blades 20 a at120° intervals about the axis of the retainer ring 20. The three inwardblades 20 a can be inserted into the three receiving areas 16 e of thelinear guide barrel 16, respectively. If the retainer ring 20 is rotatedabout the axis thereof clockwise as viewed in FIG. 6 relative to thelinear guide barrel 16 with the three inward blades 20 a being properlyinserted into the three receiving areas 16 e, respectively, each inwardblade 20 a slides into the corresponding groove 16 f. The retainer ring20 is provided on the front end face thereof with a plurality of grooves20 b which are recessed rearward, toward the linear guide barrel 16, sothat a pin face wrench (not shown) can be engaged with the recessedportions 20 b to rotate the retainer ring 20 relative to the linearguide barrel 16.

When the linear guide ring 19 is fixed to the front end of the linearguide barrel 16, firstly the three inward projections 19 a arerespectively inserted into the three receiving areas 16 e, and then thelinear guide ring 19 is rotated about the axis thereof clockwise asviewed in FIG. 6 relative to the linear guide barrel 16 so that eachinward projection 19 a slides into the corresponding groove 16 f.Subsequently, each inward projection 19 a is made to be fitted in thecorresponding recess 16 g. This engagement of each inward projection 19a with the corresponding recess 16 g determines the fixedcircumferential position of the linear guide ring 19 relative to thelinear guide barrel 16. Subsequently, the inward blades 20 a of theretainer ring 20 are respectively inserted into the three receivingareas 16 e, and then the retainer ring 20 is rotated about the axisthereof clockwise as viewed in FIG. 6 relative to the linear guidebarrel 16 so that each inward blade 20 a slides into the correspondinggroove 16 f and presses the corresponding inward projection 19 a intothe corresponding recess 16 g. This prevents the linear guide ring 19from moving in the optical axis direction relative to the linear guidebarrel 16. In this state, since each of the three inward blades 20 a ofthe retainer ring 20 is held in one of the three grooves 16 f betweenthe corresponding engaging lug 16 d and the corresponding inwardprojection 19 a, the inward blades 20 a and the engaging lugs 16 dfunction to prevent the linear guide ring 19 from coming off the frontend of the linear guide barrel 16. Between the linear guide barrel 16and the retainer ring 20 is provided a click-stop device which preventsthe retainer ring 20 from rotating counterclockwise as viewed in FIG. 6so that the retainer ring 20 cannot come off the front end of the linearguide barrel 16 after the retainer ring 20 is properly engaged with thelinear guide barrel 16. Three indentations 20 a 1 which are formed onthe retainer ring 20 and corresponding three detent 16 j which areformed on the linear guide barrel 16 to be respectively engaged with thethree indentations 20 a 1 constitute the elements of the click-stopdevice (see FIGS. 6 and 7).

Accordingly, the outward projections 19 b of the linear guide ring 19that is fixed to the front end of the linear guide barrel 16 in theabove described manner are located at predetermined specific positions(angular positions) relative to the linear guide projections 16 b. Thezoom lens is provided at the front thereof with an external barrel (ahood barrel) 25(L). The external barrel 25 is provided, on an innerperipheral surface thereof at 120° intervals about the axis of theexternal barrel 25, with three linear guide grooves 25 a which extendparallel to the optical axis O. The three outward projections 19 b ofthe linear guide ring 19 are respectively engaged with the three linearguide grooves 25 a to guide the external barrel 25 to move in theoptical axis direction without rotating about the optical axis O. Theexternal barrel 25 is provided at the rear end thereof with threeradially inward pins 25 b which are respectively engaged with threeguide grooves 18 b formed on outer peripheral surface of the second cambarrel 18 at 120° intervals about the axis thereof.

As shown in FIG. 8, each of the three guide grooves 18 b of the secondcam barrel 18 defines an assembling position (or a disassemblingposition) X at which the three inward pins 25 b of the external barrel25 are respectively inserted into or taken out of the three guidegrooves 18 b of the second cam barrel 18. Each of the three guidegrooves 18 b further defines an accommodation position, a telephotoposition and a wide-angle extremity, which determine the accommodationposition, the telephoto extremity and the wide-angle extremity of thefirst cam barrel 17, respectively. The three guide grooves 18 b areformed to move the external barrel 25 in the optical axis direction inaccordance with the rotational position of the second cam barrel 18,which rotates together with the first cam barrel 17. More specifically,the three guide grooves 18 b are formed to make the external barrel 25function as a movable lens hood so that the external barrel 25 advancesrelative to the second cam barrel 18 (i.e., the first lens group L1)when the zoom lens is set at the telephoto extremity thereof having anarrow angle of view while the external barrel 25 retreats relative tothe second cam barrel 18 when the zoom lens is set at the wide-angleextremity thereof having a wide angle of view. The external barrel 25 ispositioned in the wide-angle extremity thereof and the telephotoextremity thereof in FIG. 10 and FIG. 11, respectively.

If the external barrel 25 is pressed rearward (i.e., toward the camerabody) by an external force when the camera is in use, the compressionsprings 21 function as shock absorbers which can absorb at least part ofsuch an external force since the compression springs 21 are positionedbetween the first cam barrel 17, which guides the first and second lensgroups L1 and L2 in the optical axis direction, and the second cambarrel 18, which guides the external barrel 25 in the optical axisdirection. Such an external force is transmitted partly to the first cambarrel 17 after having been absorbed to some extent by the compressionsprings 21, which prevents large external forces from being applied tothe first cam barrel 17. Consequently, the precision of the axialposition of each of the first and second lens groups L1 and L2 isinfluenced negligibly by external forces applied to the external barrel25. In FIG. 2, the reference numeral 29(F) designates a stationaryexternal barrel which is integral with the camera body. The externalbarrel 25 advances and retreats with respect to the stationary externalbarrel 29.

The external barrel 25 is provided, at the front thereof in the radiallyinner side of the external barrel 25, with a barrier drive ring 26, sothat the barrier drive ring 26 can rotate about the optical axis O. Thebarrier drive ring 26 functions to open and shut two pairs of barrierblades 27 c and 27 d (i.e. the front pair of barrier blades 27 c and therear pair of barrier blades 27 d) by rotating about the optical axis O.The two pairs of barrier blades 27 c and 27 d together function as alens protection cover for protecting the front surface of the first lensgroup L1 from getting scratched, etc., when the digital camera is not inuse. The barrier block 27 is provided with a panel 27 b having aphotographic aperture 27 a, the aforementioned two pairs of barrierblades 27 c and 27 d supported by the panel 27 b therebehind to open andclose the photographic aperture 27 a, and two torsion springs 27 e whichconstantly bias the two pairs of barrier blades 27 c and 27 d in adirection to close the photographic aperture 27 a. The barrier block 27is further provided with an annular pressure plate 27 f which holds thetwo pairs of barrier blades 27 c and 27 d and the torsion springs 27 ebetween the panel 27 b and the pressure plate 27 f. The barrier block 27having such elements is assembled in advance as a unit. The panel 27 bis provided on a rear face thereof with two pivots 27 g (see FIGS. 13and 14) and two engaging pins 27 n. The upper front barrier blade 27 c 1of the front pair of barrier blades 27 c and the upper rear barrierblade 27 d 1 of the rear pair of barrier blades 27 d are pivoted atcorresponding one of the two pivots 27 g (the right pivot 27 g as viewedin FIG. 13), while the lower front barrier blade 27 c 2 of the frontpair of barrier blades 27 c and the lower rear barrier blade 27 d 2 ofthe rear pair of barrier blades 27 d are pivoted at the other pivot 27 g(the left pivot 27 g as viewed in FIG. 13). Each of the rear pair ofbarrier blades 27 d is constantly biased to rotate in a direction toclose the photographic aperture 27 a of the panel 27 b by thecorresponding torsion spring 27 e whose coil portion is fitted on thecorresponding engaging pin 27 n. Each of the rear pair of barrier blades27 d is provided in the vicinity of the pivoted portion thereof with adriven pin 27 h that is driven to open the corresponding rear barrierblade 27 d against the spring force of the corresponding torsion spring27 e. Each of the front pair of barrier blades 27 c is provided on anouter edge thereof with an engaging projection 27 i which extendsrearward to be engaged with the outer edge of the corresponding rearbarrier blade 27 d so that the engaging projection 27 i of each of thefront pair of barrier blades 27 c comes into engagement with the outeredge of the corresponding rear barrier blade 27 d to rotate thecorresponding front barrier blade 27 c in the direction to open thephotographic aperture 27 a together with the corresponding rear barrierblade 27 d when the corresponding rear barrier blade 27 d is driven torotate in the direction to open the photographic aperture 27 a. Theupper front barrier blade 27 c 1 is provided on a rear surface thereofwith an engaging projection 27 j, while the upper rear barrier blade 27d 1 is provided on a front surface thereof with an engaging projection27 k (see FIGS. 15A, 15B and 15C). When the upper rear barrier blade 27d 1 is driven to rotate in the direction to close the photographicaperture 27 a, the engaging projection 27 k of the upper rear barrierblade 27 d 1 is engaged with the engaging projection 27 j of the upperfront barrier blade 27 c 1 to drive the upper front barrier blade 27 c 1to rotate in the direction to close the photographic aperture 27 atogether with the upper rear barrier blade 27 d 1. Likewise, the lowerfront barrier blade 27 c 2 is provided on a rear surface thereof with anengaging projection 27 j, while the lower rear barrier blade 27 d 2 isprovided on a front surface thereof with an engaging projection 27 k(see FIGS. 15A, 15B and 15C). When the lower rear barrier blade 27 d 2is driven to rotate in the direction to close the photographic aperture27 a, the engaging projection 27 k of the lower rear barrier blade 27 d2 is engaged with the engaging projection 27 j of the lower frontbarrier blade 27 c 2 to drive the lower front barrier blade 27 c 2 torotate in the direction to close the photographic aperture 27 a togetherwith the lower rear barrier blade 27 d 2.

The pressure plate 27 f is provided with two slots 27 m through whichthe two drive pins 27 h of the rear pair of barrier blades 27 dpenetrate toward the barrier drive ring 26, respectively.

The barrier drive ring 26 is provided on the front thereof with twoprotrusions 26 b, while the external barrel 25 is provided in thevicinity of the front end thereof with corresponding two protrusions 25c (see FIGS. 16, 17 and 18). Two helical extension springs 28 arepositioned between the external barrel 25 and the barrier drive ring 26so that one and the other ends of one helical extension spring 28 arehooked on one of the two protrusions 26 b and corresponding one of thetwo protrusions 25 c, respectively, and one and the other ends of theother helical extension spring 28 are hooked on the other protrusion 26b and the other protrusion 25 c, respectively. The spring force of eachhelical extension spring 28 is stronger than the spring force of eachtorsion spring 27 e. The barrier drive ring 26 is constantly biased bythe two helical extension springs 28 to rotate in the direction to openthe two pairs of barrier blades 27 c and 27 d. The barrier drive ring 26is provided on the front thereof with two protrusions 26 c which can berespectively engaged with the two drive pins 27 h of the rear pair ofbarrier blades 27 d to open the two pairs of barrier blades 27 c and 27d. When the barrier drive ring 26 is rotated to the rotational limitthereof by the spring force of the helical extension springs 28, each ofthe two protrusions 26 c is engaged with the corresponding driven pin 27h to push the same in the direction to open the corresponding rearbarrier blade 27 d against the spring force of the corresponding torsionspring 27 e, so that the corresponding front barrier blade 27 c alsoopens via the engaging projection 27 i thereof (see FIGS. 15A, 15B and15C).

On the other hand, the barrier drive ring 26 is provided with a drivenlever 26 a which extends from the rim of the barrier drive ring 26toward the second cam barrel 18 to be engaged with, and disengaged from,a rotation transfer recess 18 c formed on an outer peripheral surface ofthe second cam barrel 18 (see FIGS. 8, 9 and 16). Since the barrierdrive ring 26 is supported by the external barrel 25 to be rotatableabout the optical axis O relative to the external barrel 25, butimmovable in the optical axis direction relative to the external barrel25, the barrier drive ring 26 moves toward and away from the rotatingsecond cam barrel 18 if the external barrel 25 linearly moves in theoptical axis direction due to the engagement of the inward pins 25 b ofthe external barrel 25 with the guide grooves 18 b of the second cambarrel 18 as can be seen in FIGS. 8 and 9. The driven lever 26 a and therotation transfer recess 18 c are apart from each other when positionedwithin a photographing range (i.e., between the telephoto extremity andthe wide-angle extremity) as shown in FIG. 8. When the zoom barrelretreats from the telephoto extremity thereof to the accommodationposition thereof, the driven lever 26 a approaches the rotation transferrecess 18 c and is then engaged with the rotation transfer recess 18 cto apply a force to the barrier drive ring 26 to rotate the same in thedirection to close the two pairs of barrier blades 27 c and 27 d. Whenthe barrier drive ring 26 rotates to the rotational limit thereofagainst the spring force of the helical extension springs 28, each ofthe protrusions 26 c of the barrier drive ring 26 disengages from thedrive pins 27 h of the corresponding rear barrier blade 27 d. As aresult, each of the rear pair of barrier blades 27 d closes by thespring force of the corresponding torsion spring 27 e, so that each ofthe front pair of barrier blades 27 c also closes via the correspondingengaging projections 27 j and 27 k to thereby close the photographicaperture 27 a (see FIG. 14). Conversely, when the zoom barrel advancesfrom the accommodation position thereof to the telephoto extremitythereof, the driven lever 26 a moves forwards and then disengages fromthe rotation transfer recess 18 c to thereby allow the barrier drivering 26 to rotate in the direction to open the two pairs of barrierblades 27 c and 27 d by the spring force of the helical extensionsprings 28. As a result, each of the protrusions 26 c of the barrierdrive ring 26 is engaged with the drive pin 27 h of the correspondingrear barrier blade 27 d to push the same in the direction to open thecorresponding front barrier blade 27 c via the corresponding engagingprojection 27 i to thereby open the two pairs of barrier blades 27 c and27 d. Accordingly, as can be understood by the above description, thetwo pairs of barrier blades 27 c and 27 d are driven to open and closeby rotation of the barrier drive ring 26. It should be noted that thebarrier drive ring 26 has only one driven lever 26 a, whereas the secondcam barrel 18 has three rotation transfer recesses 18 c formed at 120°intervals about the axis of the second cam barrel 18. One rotationtransfer recess 18 c which is actually used is freely selected from thethree rotation transfer recesses 18 c during assembly.

The external barrel 25 that is guided in the optical axis directionmoves forward and rearward in the optical axis direction by rotation ofthe second cam barrel 18 in the above described manner. On the otherhand, the first and second lens groups L1 and L2 move forward andrearward in the optical axis direction by rotation of the first cambarrel 17. FIG. 12 shows the axial position of the sensitive surface(image plane) of the CCD 12 a on which subject images are formed throughthe photographic optical system, and the variations in the axialpositions of the first lens group L1 (the principal point of the firstlens group L1), the second lens group L2 (the principal point of thefirst lens group L2), and the barrier block 27 fixed to the front end ofthe external barrel 25 (more specifically, the photographic aperture 27a formed on the panel 27 b of the barrier block 27), when the zoom lensis driven from the accommodation position to the wide-angle extremityvia the telephoto extremity. The contours of the first and second camgrooves 17C1 and 17C2 of the first cam barrel 17 and the guide grooves18 b of the second cam barrel 18 are determined so that the first lensgroup L1, the second lens group L2 and the barrier block 27 move in theoptical axis direction to have the moving paths shown in FIG. 12. Thephotographic aperture 27 a has a generally rectangular shape as viewedfrom the front of the digital camera. The angle of view in the diagonaldirection of the photographic aperture 27 a is greater than the angle ofview in the lateral (horizontal) direction of the photographic aperture27 a, while the angle of view in the lateral direction of thephotographic aperture 27 a is greater than the angle of view in thelongitudinal (vertical) direction of the photographic aperture 27 a.InFIG. 10, an incident light ray S on the zoom lens along the angle ofview in the longitudinal direction of the photographic aperture 27 a, anincident light ray M on the zoom lens along the angle of view in thelateral direction of the photographic aperture 27 a, and an incidentlight ray L on the zoom lens along the angle of view in the diagonaldirection of the photographic aperture 27 a are shown by two-dot chainlines.

A light shield barrel 26 d which extends from the inner edge of thebarrier drive ring 26 to the front end of the outer peripheral surfaceof the first lens frame 22 is adhered to the inner edge of the barrierdrive ring 26 by an adhesive. The light shield barrel 26 d isrotationally symmetrical about the optical axis O, so that the shieldingcharacteristics of the light shield barrel 26 d do not vary even if thelight shield barrel 26 d rotates forwardly and reversely together withthe barrier drive ring 26 about the optical axis O.

Almost all the above mentioned elements of the zoom lens except for eachspring, the feed screw 10 e, the set screws 23 f, the follower pins 22d, the follower pins 23 d, the shutter block 24, the radially inwardpins 25 b, the flexible coding plate 14 and the brush 15 are made ofsynthetic resin. Although each lens element of the first, second andthird lens groups L1, L2 and L3 can be made of a plastic, at least thefrontmost lens element is preferably a glass lens for the purpose ofpreventing the front surface of the first lens group L1 from beingscratched.

In the above illustrated embodiment, although the third lens group L3functions as focusing lens group, the zoom lens can be modified so thatthe first lens group L1 or the second lens group L2 functions asfocusing lens group. In the case where the second lens group L2functions as focusing lens group, the shutter block can be modified tohave an auto-focusing function. Such a shutter block is well-known inthe art.

In the above described embodiment of the zoom lens, each of the firstand second lens frames 22 and 23, which respectively hold the first andsecond lens groups L1 and L2, is guided linearly in the optical axisdirection without rotating about the optical axis O by the engagement ofeach of the three square projections 22 c and corresponding each of thethree square projections 23 c with each common corresponding linearguide slot of the three linear guide slots 16 c. At the same time, eachfollower pin 22 d penetrates through the corresponding linear guide slot16 c of the linear guide barrel 16 to be engaged with the correspondingfirst cam groove 17C1 of the first cam barrel 17, which is fitted on thelinear guide barrel 16 to be rotatable about the optical axis relativeto linear guide barrel 16, while each follower pin 23 d penetratesthrough the corresponding linear guide slot 16 c of the linear guidebarrel 16 to be engaged with the corresponding second cam groove 17C2 ofthe first cam barrel 17.

According to such a lens frame guiding structure, eccentricity betweenthe first and second lens groups L1 and L2 does not occur easily. Morespecifically, if the linear guide barrel 16 is deformed slightly forsome reason, eccentricity between the first and second lens groups L1and L2 does not occur in the case that each of the three squareprojections 22 c and corresponding each of the three square projections23 c are engaged with each common corresponding linear guide slot of thethree linear guide slots 16 c, as compared with the case that each ofthe three square projections 22 c and corresponding each of the threesquare projections 23 c are engaged with different linear guide grooves.In addition, the first cam barrel 17 is fitted on the linear guidebarrel 16, while the three follower pins 22 d and the three followerpins 23 d are respectively engaged with the first cam grooves 17C1 andthe second cam grooves 17C2. Due to this structure, even if the firstcam barrel 17 is deformed slightly for some reason, and if the first andsecond lens frames 22 and 23 deviate from the optical axis O by beingrespectively pressed radially by the bottoms of the first and second camgrooves 17C1 and 17C2 due to the bottom of each of the first and secondcam grooves 17C1 and 17C2 not being positioned precisely on a commonimaginary cylinder, the first and second lens frames 22 and 23 deviatein the same radial direction. As a consequence, eccentricity between thefirst and second lens groups L1 and L2 does not occur easily. As hasbeen described above, in the photographing lens system of a digitalcamera, the influence that eccentricity or tilt of one or more lensgroups relative to another lens group or groups has upon the opticalperformance of the photographing optical system is larger than theinfluence of a deviation of one or more lens groups in the optical axisdirection relative to another lens group or groups. Accordingly, withthe lens frame guiding structure which makes eccentricity between lensgroups difficult to occur, an excellent optical performance of thephotographing optical system can be maintained.

More than one square projection 22 c of the first lens frame 22, each ofwhich has one follower pin 22 d, can be provided at predeterminedintervals in a circumferential direction, while more than one squareprojection 23 c of the second lens frame 23, each of which has onefollower pin 23 d, can be provided at predetermined intervals in acircumferential direction. Likewise, more than one linear guide slot 16c of the linear guide barrel 16 can be provided at predeterminedintervals in a circumferential direction, while more than one pair ofcam grooves (i.e., one first cam groove 17C1 and the correspondingsecond cam groove 17C2) can be provided at predetermined intervals in acircumferential direction. However, in the case of three squareprojections 22 c, each having one follower pin 22 d, being provided at120° intervals; three square projections 23 c, each having one followerpin 23 d, being provided at 120° intervals; three linear guide slot 16 cbeing provided at 120° intervals; and three pairs of cam grooves 17C1and 17C2 being provided at 120° intervals just like the aboveillustrated embodiment, the first and second lens frames 22 and 23 canbe easily coupled to the linear guide barrel 16 and the first cam barrel17 in a well-balanced manner with minimum eccentricity between the firstand second lens frames 22 and 23.

The present invention can be applied to not only the above illustratedembodiment of the zoom lens having particular structure but also anyother zoom lens, as long as the zoom lens has a plurality of lensframes, a linear guide barrel and a cam barrel.

Although the present invention is applied to the zoom lens of a digitalcamera, the present invention can be applied not only to a zoom lens ofa digital camera, but also a zoom lens of a lens shutter type camera.

As can be understood from the foregoing, according to the presentinvention, in a zoom lens having a plurality of lens frames, a linearguide barrel and a cam barrel, a lens frame guiding mechanism whichmakes an eccentricity between lens groups hard to occur to thus preventthe optical performance of the zoom lens optical system fromdeteriorating due to the eccentricity can be obtained.

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

What is claimed is:
 1. A lens frame guiding mechanism of a zoom lens,comprising: a plurality of lens frames each having a plurality ofprojections which extend radially outwards at predetermined intervals ina circumferential direction, wherein a cam follower is formed on each ofsaid projections; a linear guide barrel provided around said pluralityof lens frames, wherein said linear guide barrel is guided along anoptical axis of said zoom lens without rotating; a plurality of linearguide slots formed on said linear guide barrel to extend parallel tosaid optical axis, wherein the number of said plurality of linear guideslots corresponds to the number of said plurality of projections of eachof said lens frames so that said plurality of projections of each ofsaid lens frames are respectively engaged in said plurality of linearguide slots to be slidable in a direction of said optical axis; a cambarrel fitted outside said linear guide barrel to be rotatable aboutsaid optical axis relative to said linear guide barrel; and a pluralityof bottomed cam grooves formed on an inner peripheral surface of saidcam barrel for each of said plurality of lens frames, in which saidplurality of cam followers of a corresponding lens frame of saidplurality of lens frames are respectively engaged, wherein the profilesof said cam grooves for one of said plurality of lens frames isdifferent from the profiles of said cam grooves for the other of saidplurality of lens frames; wherein said plurality of lens frames aremoved in the direction of said optical axis, without rotating about saidoptical axis, to change a focal length of said zoom lens via rotation ofsaid cam barrel.
 2. The lens frame guiding mechanism according to claim1, wherein the number of said projections of each of said lens frames,the number of said linear guide slots of said linear guide barrel, andthe number of said bottomed cam grooves of said cam barrel are three,respectively arranged at 120° equi-angular intervals.
 3. The lens frameguiding mechanism according to claim 1, wherein said cam barrel isfitted on said linear guide barrel so as to be immovable in saiddirection of said optical axis relative to said linear guide barrel. 4.The lens frame guiding mechanism according to claim 1, wherein each ofsaid plurality of projections is formed to have opposite faces extendingparallel to each other so that said opposite faces are respectively insliding contact with side faces of a corresponding linear guide slot ofsaid plurality of linear guide slots.
 5. The lens frame guidingmechanism according to claim 1, wherein said zoom lens is incorporatedin a digital camera.
 6. A lens frame guiding mechanism of a zoom lens,comprising: a first lens frame having a first group of three projectionsextending radially outwards at equi-angular intervals, each of saidfirst group of three projections having a first cam follower; a secondlens frame having a second group of three projections extending radiallyoutwards at equi-angular intervals, each of said second group of threeprojections having a second cam follower; a linear guide barrel providedaround said first lens frame and said second lens frame, and guided in adirection of an optical axis of said zoom lens without rotating aboutsaid optical axis; three linear guide slots formed on said linear guidebarrel so as to extend parallel to said optical axis, said first groupof three projections and said second group of three projections beingslidably engaged in said three linear guide slots, respectively; a cambarrel fitted on said linear guide barrel to be rotatable about saidoptical axis relative to said linear guide barrel; a first group ofthree cam grooves which are formed on an inner peripheral surface ofsaid cam barrel so that said three first cam followers are respectivelyengaged in said first three cam grooves; and a second group of three camgrooves which are formed on said inner peripheral surface of said cambarrel so that said three second cam followers are respectively engagedin said second group of three cam grooves, wherein said first and secondlens frames are moved in said direction of said optical axis withoutrotating about said optical axis in a predetermined moving manner tochange a focal length of said zoom lens by rotation of said cam barrel.